Background Checks

I am interviewing with a company for the position of an HR assistant. I have 3 felony charges but no convictions from 12 years ago. They ended as "dismissed without leave after deferred prosecution", again let me reiterate there was no conviction. The deferred prosecution was performing community service hours. The charges stemmed from forging checks when I was 18. I am now in the process of having an attorney expung/permanently remove them from my record, however, this could take up to four months. I know that I can honestly answer "No" to the question on the application that asks "Have you ever been convicted of a felony" but I also know that when they do a criminal background check these three charges will appear because the expungement process is not complete. What suggestions do you have for me? Should I be open and honest with them in the beginning or wait until after they pull my background and then explain? Also, should I let the potential employer know that this record will no longer exist in a few months as I am in the process I having this permanently removed? This did happen 12 years ago when I was 18. I am now 30 and have just earned by Bachelor's degree, graduating with Honors, I am also attending grad school this fall. Help, I screwed up long time a go but am a different person today. Do you have any advice? Thank you